The present invention relates to an improved cutoff saw that is capable of optimizing yield in accordance with predefined yield criteria in an automatic board crosscutting operation. More specifically, it concerns board handling speed and accuracy improvements to a continuous, driven belt conveyor-type cutoff saw having a first belt conveyor disposed in frictional engagement with an upper surface of a board both upstream and downstream of the saw by the provision of a second continuous belt conveyor disposed below the first belt conveyor along a substantial extent of the same and upstream from the cutoff station in a board infeed zone, with the second belt conveyor being driven synchronously with the first belt conveyor. The first belt conveyor includes a belt and a pair of rollers mounted for rotation on a pivotal arm that is urged by tension in the first belt into a position whereby the board is grippingly engaged between the first and second belt conveyors.
Prior art automatic board cutoff saws have provided for the positive hold-down of boards both upstream and downstream from a vertically reciprocable circular saw blade that, while the board is stopped at a predetermined location to make a desired crosscut, is raised to make a planar cut therein. One such advanced automatic cutoff saw is the Series III Ultimizers.TM. cutoff saw made by Ultimizers, Inc. of Boring, Oreg., which is the assignee of rights in the present application. The Series III cutoff saw uses a continuous belt conveyor to advance a board of nominal thickness through, and to hold down the board in, the cutoff station by frictionally engaging it along substantial lengthwise extents on either side of the cutoff station. The Series III saw's continuous, overhead conveyor belt avoids the vertically reciprocating path of the circular saw blade by traversing a path therearound, leaving all but a marginal region of the board adjacent the intended cut in continuous frictional engagement by the belt conveyor throughout the infeed, cut and advance phases of automatic operation.
In the operation of conventional cutoff saws, boards may be automatically or manually mark sensed, e.g. using a special crayon-like marker to indicate desired cut lengths or locations, or to indicate undesirable board sections, e.g. the location of a knot, wane or bend. By appropriately programming the controller, `intelligent` determinations automatically are made regarding the optimal series of cuts that will maximize a particular board's yield. An automatic mark-sense reader near the infeed location of the Series III cutoff saw reads the coded markings and the controller controls the belt conveyor to start, advance and stop the conveyor belt, and thus the board frictionally engaged thereby, as it approaches, traverses and departs the cutoff station. With such automatic cutoff saws, it has been possible to maintain high accuracy and repeatability in board handling and crosscutting at relatively high linear speeds, e.g. up to approximately thirty feet per second (30-fps).
Despite the high quality and throughput of automatic cutoff saws such as the Series III Ultimizers.TM. cutoff saw, there remains room for improvement in their board handling technique, especially at the infeed and outfeed locations. Proper placement, alignment and control of a board significantly impacts the accuracy of crosscuts made thereon, and has the potential of maximizing yield and minimizing waste. The infeed and outfeed stations are locations where jamming frequently occurs, especially as the linear speed of the belt conveyor is increased to improve board throughput. Heretofore, these problems, to which even the state of the art Ultimizer.TM. Series III cutoff saw is subject, remained unsolved.
Accordingly, it is an object of the present invention to achieve an increase in linear speed on overhead belt conveyors used in optimizing cutoff saws, while greatly improving positional accuracy.
It is another important object of the invention to reduce the frequency with which boards jam in such cutoff saws.
Another important object is to bring about such improvements in such manner that existing installations can be retrofitted with the improvements easily and cost effectively.
In brief summary, the invention in its preferred embodiment takes the form of a second belt conveyor disposed beneath the overhead belt conveyor in the infeed region of the cutoff saw and driven synchronously therewith, wherein the second belt conveyor extends longitudinally of, and thus frictionally engages over a substantial length, the board therein. Means for synchronizing the linear speed of the second, lower belt conveyor, in relation to that of the first, overhead or upper belt conveyor is accomplished by a controller that provides synchronization signals to the servo motors that drive each belt of the belt conveyors. Preferably, a pair of rollers of the upper belt conveyor are mounted for rotation on a pivotable member the pivotal position of which is determined by tension in the upper belt, wherein the member's position urges one of the rollers and thus the first belt into frictional engagement with a board, thereby grippingly engaging the board, which may be slightly undersized in thickness, between the upper and the lower belts. At the outfeed location of the crosscut saw, the throat is opened slightly by the reduced dimensioning of one of the upper conveyor's rollers to accommodate a board-in-process the leading end of which may be slightly elevated as the vertically reciprocable circular saw is in its raised position. The result of these and other improvements is greatly improved board control and the positional and orientational accuracy of crosscuts made therein.
These and other objects and advantages of the invention will be better understood by reference to the accompanying drawings and the following description.